Conductive carbon black modified lithium iron phosphate electrode material and preparation method thereof

Abstract

This invention provides a conductive carbon black-modified lithium iron phosphate electrode material and its preparation method. The material uses a transition metal-doped LiFePO4 matrix combined with a specific ratio of dual-scale conductive carbon black, achieving stable interfacial bonding through P-C covalent bonds and constructing a gradient pore structure. During the preparation process, key technologies such as optimized sintering, carbon black surface modification, programmed current-controlled pore formation, and plasma treatment are employed to enable the material to possess both high electronic conductivity and excellent ion transport performance. The resulting electrode material exhibits high specific capacity, excellent rate performance, and long cycle life, making it suitable for high-power lithium-ion battery cathodes and solving the problems of insufficient conductivity and poor interfacial stability in traditional lithium iron phosphate materials.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and relates to a conductive carbon black modified lithium iron phosphate electrode material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, is widely used in the field of power batteries due to its advantages such as high safety, long cycle life, and abundant raw materials. However, this material faces two major technical bottlenecks: one is its extremely low intrinsic electronic conductivity (approximately 10⁻⁶ ppm). -8 Secondly, the lithium-ion diffusion rate is slow (approximately 10 S / cm). -14 cm 2 These characteristics result in poor rate performance of the material, especially under high-rate charge-discharge conditions, where capacity decay is significant. Currently, the industry mainly improves its conductivity through carbon coating and the addition of conductive agents. However, conventional carbon coating processes often lead to uneven coating layers, and excessively thick carbon layers can actually hinder lithium-ion transport. Simple mechanical mixing of conductive agents, on the other hand, makes it difficult to construct a continuous and efficient conductive network. Furthermore, existing technologies lack sufficient control over the material's pore structure, affecting electrolyte wetting and ion transport efficiency. These factors collectively limit the performance of lithium iron phosphate materials in high-power applications.

[0003] CN 112694078A discloses a graphene-coated lithium iron phosphate composite material and its preparation method. The preparation method includes: coating graphene oxide and lithium iron phosphate by spray drying or evaporation drying to obtain graphene-coated lithium iron phosphate solid; and subjecting the obtained graphene-coated lithium iron phosphate solid to heat treatment to obtain the graphene-coated lithium iron phosphate composite material. The ratio of the graphene oxide sheet diameter to the D50 of the lithium iron phosphate is 0.05–40. Although the composite material improves conductivity, graphene is expensive, and the coating layers are prone to stacking, resulting in limited improvement in actual rate performance.

[0004] CN107195979A discloses a power energy storage polymer lithium-ion battery, which is composed of 2-5 wound cells connected in parallel and then encapsulated with an aluminum-plastic film. Each cell includes a positive electrode, a separator, a negative electrode, an electrolyte, and tabs. The positive electrode is prepared by coating a positive electrode slurry prepared by a pre-milling process. The negative electrode is prepared by coating a negative electrode slurry prepared by a pre-milling process. Each cell, including the positive and negative electrode tabs, uses a carbon nanotube / carbon black composite conductive agent. Although the lithium-ion battery constructs a three-dimensional conductive network, the interfacial bonding problem between LiFePO4 and carbon materials has not been solved, and interfacial delamination is prone to occur during cycling.

[0005] CN112151743A provides a method for creating pores in a thick electrode, along with the product and its applications. The method involves coating a slurry with a viscosity of 6000 mPa·s to 9000 mPa·s onto the surface of a current collector with a surface roughness Ra ≥ 1 μm, followed by drying to obtain the thick electrode. While the method partially solves the problems of poor electrolyte wettability and long lithium-ion migration paths, it suffers from uneven pore distribution and a lack of gradient design, resulting in limited lithium-ion transport at high rates and insufficient capacity retention. Summary of the Invention

[0006] The purpose of this invention is to provide a conductive carbon black-modified lithium iron phosphate electrode material and its preparation method, which features high electronic conductivity, excellent rate performance, and long cycle life. By enhancing intrinsic conductivity through specific Li vacancy regulation and transition metal doping, and constructing a three-dimensional conductive network using nano / micro carbon black hierarchical methods, combined with plasma-induced interface bonding technology and CO2-controlled pore-forming process, the material simultaneously possesses comprehensive advantages such as high compaction density, excellent rate performance, and ultra-long cycle life, effectively solving the technical problems of poor conductivity and insufficient high-rate performance in traditional lithium iron phosphate materials.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a conductive carbon black-modified lithium iron phosphate electrode material, comprising:

[0009] Li 1-x Fe 1+x The matrix is ​​PO4, where 0.01 ≤ x ≤ 0.05, and the Fe sites are doped with 1-3 at% Mn. 2+ or Co 2+ ;

[0010] A conductive carbon black composition comprising 60-70 wt% nano-carbon black and 30-40 wt% micron-sized carbon black, wherein the nano-carbon black has a D50 ≤ 100 nm and a specific surface area ≥ 800 m². 2 / g, the micron-sized carbon black has a D50 of 1-3μm and a specific surface area ≥60m². 2 / g;

[0011] The Li 1-x Fe 1+x The PO4 particles are covalently bonded to conductive carbon black via PC, with a bond density ≥ 0.5 bonds / nm. 2 ;

[0012] The material has a gradient pore structure, with a surface porosity of 25-30% and a pore size of 50-100 nm, and a core porosity of 15-20% and a pore size of 200-300 nm.

[0013] The conductive carbon black-modified lithium iron phosphate electrode material provided by this invention achieves precise control of Li... 1-x Fe 1+x Li vacancies in PO4 (0.01≤x≤0.05) and 1-3 at.% Mn doped at Fe sites. 2+ / Co 2+ Defect energy levels are introduced into the crystal structure; Li vacancies increase lithium-ion diffusion channels, while Mn... 2+ / Co 2+ Fe replacement 2+ Subsequently, its variable valence state provides additional electronic transition pathways, synergistically increasing the intrinsic electronic conductivity of the material to 10. -4 S / cm, lithium-ion diffusion coefficient increased to 10 -12 cm 2 / s.

[0014] Preferably, the Li 1-x Fe 1+x PO4 is prepared by solid-state method or hydrothermal method, wherein the molar ratio of Li:Fe is (0.95-0.99):(1.01-1.05).

[0015] Preferably, the nano carbon black is acetylene black, the micron carbon black is SuperP, and both are surface modified with a silane coupling agent.

[0016] The conductive carbon black-modified lithium iron phosphate electrode material provided by this invention uses acetylene black as nano-carbon black and SuperP as micron-carbon black, and performs surface modification treatment with a silane coupling agent. In terms of material selection, acetylene black, with its nano-sized particle size and high specific surface area, can effectively fill the gaps between active materials and construct dense conductive pathways; while SuperP, as a micron-sized conductive agent, plays a key role in connecting the conductive network. The two are combined in an optimal ratio to form a complementary conductive system. The surface modification treatment uses silane coupling agent KH-550, and uniform coating is achieved through a precisely controlled ball milling process. During the modification process, one end of the silane coupling agent molecule forms a chemical bond with the carbon black surface, and the other end establishes a connection with the active material. This dual bonding effect significantly enhances the interfacial bonding strength. The modified conductive network not only has excellent electronic conductivity but also exhibits good structural stability.

[0017] This technical solution fundamentally solves the problems of poor interfacial contact and easy damage to the conductive network inherent in traditional physical mixing methods through chemical bonding. The modified electrode material maintains high conductivity while significantly improving its interfacial stability and mechanical strength, laying a solid foundation for excellent electrochemical performance. This innovative surface modification method provides a new technical approach for the development of high-performance lithium-ion battery electrode materials.

[0018] In a second aspect, the present invention provides a method for preparing a conductive carbon black modified lithium iron phosphate electrode material as described in the first aspect, comprising the following steps:

[0019] (1) According to Li 1-x Fe 1+x The raw materials were mixed in stoichiometric proportions with PO4, and Mn was added. 2+ or Co 2+ Salt was sintered at 650-750℃ for 6-8 hours to obtain doped LiFePO4 powder;

[0020] (2) Mix nano carbon black and micron carbon black in a certain proportion, add silane coupling agent and ball mill for modification for 1.8-2.2h;

[0021] (3) The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a speed of 480-520 rpm for 2.8-3.2 h;

[0022] (4) Mix the mixture obtained in step (3) with the composite pore-forming agent, and introduce CO2 gas during the programmed temperature rise process, wherein the CO2 flow rate is 4.5-5.5 mL / min at 200-300℃ and 10-20 mL / min at 300-400℃;

[0023] (5) The product obtained in step (4) is treated in an argon plasma environment with a power of 230-270W for 25-35 minutes.

[0024] The method for preparing conductive carbon black modified lithium iron phosphate electrode material provided by this invention utilizes plasma-induced PC bonding. During argon plasma treatment, high-energy particle bombardment causes the PO43- bonds on the LiFePO4 surface to break, forming dangling P atoms that bond with carbon black sp. 2 Carbon's π electron cloud undergoes covalent bonding to form PC bonds with a bond energy of 326 kJ / mol; the bond density is ≥0.5 bonds / nm. 2 This improves interface stability by 3 times, and the carbon black shedding rate during the cycle is less than 1%.

[0025] Preferably, the Mn in step (1) 2+ The salt is manganese acetate, and the Co 2+ The salt is cobalt nitrate, and the amount added is 1-3% of the molar amount of Fe.

[0026] Preferably, the silane coupling agent in step (2) is KH-550, and the amount added is 0.5-1% of the total mass of carbon black.

[0027] Preferably, the composite pore-forming agent in step (4) is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of (2.8-3.2):1, and the total amount of the composite pore-forming agent added is 8-12% of the mass of LiFePO4.

[0028] The method for preparing conductive carbon black modified lithium iron phosphate electrode material provided by the present invention controls the CO2 flow rate in stages and utilizes the stepwise decomposition characteristics of NH4HCO3 and ammonium oxalate to form densely packed small pores on the surface and through-pores in the core layer by directional etching of CO2 gas flow. This structure shortens the electrolyte wetting time and has a porosity gradient distribution, thus ensuring the strength of the electrode structure.

[0029] Preferably, the purity of the CO2 gas in step (4) is ≥99.5%.

[0030] Preferably, the pressure of the argon plasma treatment in step (5) is 50-100 Pa.

[0031] Thirdly, the present invention provides a lithium-ion battery positive electrode, made of conductive carbon black modified lithium iron phosphate electrode material as described in the first aspect, wherein the compaction density of the positive electrode is ≥2.7 g / cm³. 3 Capacity retention at 5C rate is ≥90%, and capacity retention after 3000 cycles is ≥85%.

[0032] The beneficial effects of this invention are:

[0033] (1) The conductive carbon black modified lithium iron phosphate electrode material provided by the present invention improves the intrinsic electronic conductivity to 10 through the synergistic effect of Li vacancy regulation and Mn / Co doping. -4 S / cm, lithium-ion diffusion coefficient increased to 10 -12 cm 2 / s;

[0034] (2) The present invention provides a method for preparing conductive carbon black modified lithium iron phosphate electrode material, which uses nano / micro carbon black hierarchically to construct a gradient conductive network, combined with plasma-induced PC bonding, to achieve an electrode compaction density of 2.7 g / cm³. 3 The interface impedance is reduced by 60%;

[0035] (3) The conductive carbon black modified lithium iron phosphate electrode material provided by the present invention uses CO2 dynamic control pore-forming process to form gradient pores, electrolyte wetting time ≤3s, 5C capacity retention rate ≥90%, and 3000 cycles capacity retention rate ≥85%. Detailed Implementation

[0036] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0037] In one specific embodiment, the present invention provides a conductive carbon black modified lithium iron phosphate electrode material, comprising a LiFePO4 matrix, doping elements, and a modified carbon black conductive agent, wherein the surface of the LiFePO4 matrix is ​​coated with a carbon layer, the doping elements are Mn and Co, and the doping amounts of Mn and Co are 1-3% of the molar amount of Fe, respectively; the modified carbon black conductive agent is obtained by mixing nano-carbon black and micron-carbon black in a certain proportion and modifying it with silane coupling agent KH-550, wherein the amount of KH-550 added is 0.5-1% of the total mass of carbon black.

[0038] In another specific embodiment, the present invention provides a method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described above, the method specifically comprising: (1) mixing iron salt, lithium salt, phosphorus source and dopants manganese acetate and cobalt nitrate, wherein Mn 2+ and Co 2+ The addition amount is 1-3% of the Fe molar amount. The precursor is prepared by spray drying and sintered at 600-800℃ for 5-7h under an inert atmosphere to obtain carbon-coated LiFePO4 powder; (2) Nano carbon black and micron carbon black are mixed in proportion, and 0.5-1% of KH-550 silane coupling agent of total carbon black mass is added for ball milling modification treatment for 1.8-2.2h; (3) The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a speed of 480-520rpm for 2.8-3.2h; (4) The mixture obtained in step (3) is mixed with the carbon black obtained in step (2) and then processed in a planetary ball mill at a speed of 480-520rpm for 2.8-3.2h. The compound is mixed with a composite pore-forming agent, wherein the composite pore-forming agent is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of 2.8-3.2:1, and the amount added is 8-12% of the mass of LiFePO4. During the programmed temperature rise process, CO2 gas with a purity ≥99.5% is introduced, wherein the CO2 flow rate is 4.5-5.5 mL / min at 200-300℃ and 10-20 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment of 50-100Pa with a power of 230-270W for 25-35min.

[0039] Example 1

[0040] This embodiment provides a conductive carbon black-modified lithium iron phosphate electrode material, including Li 0.97 Fe 1.03 PO4 matrix with 2 at% Mn doped at Fe sites. 2+The conductive carbon black composition comprises 65 wt% nano-carbon black and 35 wt% micron-sized carbon black. The nano-carbon black has a D50 of 80 nm and a specific surface area of ​​850 m². 2 / g, the D50 of micron-sized carbon black is 2μm and its specific surface area is 70m². 2 / g. Li 0.97 Fe 1.03 The PO4 particles are covalently bonded to conductive carbon black via PC bonds, with a bonding density of 0.6 bonds / nm. 2 The material has a gradient porosity structure, with a surface porosity of 28% and a pore size of 75 nm, and a core porosity of 18% and a pore size of 250 nm.

[0041] This embodiment also provides a method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described above, including: (1) according to Li 0.97 Fe 1.03 The raw materials were mixed in stoichiometric ratio with PO4, and 2 at% manganese acetate was added. The mixture was sintered at 700℃ for 7 h to obtain doped LiFePO4 powder. Nano carbon black and micron carbon black were mixed in a ratio of 65:35, and 0.8% KH-550 silane coupling agent was added for ball milling modification treatment for 2 h. The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) were treated in a planetary ball mill at a speed of 500 rpm for 3 h. The mixture obtained in step (3) was combined with composite pore-forming material. The agent is mixed, and the composite pore-forming agent is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of 3:1, and the total addition amount is 10% of the mass of LiFePO4. During the programmed temperature rise process, 99.5% pure CO2 gas is introduced, with a CO2 flow rate of 5 mL / min at 200-300℃ and a CO2 flow rate of 15 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment of 75 Pa with a power of 250 W for 30 min.

[0042] Example 2

[0043] This embodiment provides a conductive carbon black-modified lithium iron phosphate electrode material, including Li 0.99 Fe 1.01 PO4 matrix, wherein 1 at% Co is doped at Fe sites. 2+ The conductive carbon black composition comprises 60 wt% nano-carbon black and 40 wt% micron-sized carbon black, wherein the nano-carbon black has a D50 of 100 nm and a specific surface area of ​​800 m². 2 / g, the D50 of micron-sized carbon black is 1μm and its specific surface area is 60m². 2 / g. Li 0.99 Fe 1.01 The PO4 particles are covalently bonded to conductive carbon black via PC bonds, with a bonding density of 0.5 bonds / nm.2 The material has a gradient porosity structure, with a surface porosity of 25% and a pore size of 50 nm, and a core porosity of 15% and a pore size of 200 nm.

[0044] This embodiment also provides a method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described above, including: (1) according to Li 0.99 Fe 1.01 (1) Mix raw materials in stoichiometric ratio with PO4 and add 1 at% cobalt nitrate, sinter at 650℃ for 8 h to obtain doped LiFePO4 powder; (2) Mix nano carbon black and micron carbon black in a ratio of 60:40, add 0.5% KH-550 silane coupling agent and ball mill for modification treatment for 1.8 h; (3) Treat the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) in a planetary ball mill at a speed of 480 rpm for 2.8 h; (4) Mix the mixture obtained in step (4) Mix with a composite pore-forming agent, which is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of 2.8:1, and the total addition amount is 8% of the mass of LiFePO4. During the programmed temperature rise process, CO2 gas with a purity of 99.5% is introduced, wherein the CO2 flow rate is 4.5 mL / min at 200-300℃ and 10 mL / min at 300-400℃; (5) The product obtained in step (4) is treated with argon plasma at 50 Pa and a power of 230 W for 25 min.

[0045] Example 3

[0046] This embodiment provides a conductive carbon black-modified lithium iron phosphate electrode material, including Li 0.95 Fe 1.05 PO4 matrix with 3 at% Mn doped at Fe sites. 2+ The conductive carbon black composition comprises 70 wt% nano-carbon black and 30 wt% micron-sized carbon black. The nano-carbon black has a D50 of 50 nm and a specific surface area of ​​900 m². 2 / g, the D50 of micron-sized carbon black is 3μm and its specific surface area is 80m². 2 / g;Li 0.95 Fe 1.05 The PO4 particles are covalently bonded to conductive carbon black via PC bonds, with a bonding density of 0.7 bonds / nm. 2 The material has a gradient porosity structure, with a surface porosity of 30% and a pore size of 100 nm, and a core porosity of 20% and a pore size of 300 nm.

[0047] This embodiment also provides a method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described above, including: (1) according to Li 0.95 Fe 1.05(1) Mix raw materials in stoichiometric ratio with PO4 and add 3 at% manganese acetate, sinter at 750℃ for 6 h to obtain doped LiFePO4 powder; (2) Mix nano carbon black and micron carbon black in a ratio of 70:30, add 1% KH-550 silane coupling agent and ball mill for modification treatment for 2.2 h; (3) Treat the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) in a planetary ball mill at a speed of 520 rpm for 3.2 h; (4) Mix the mixture obtained in step (3) with the modified carbon black obtained in step (2) and the modified carbon black obtained in step (3) with the modified carbon black obtained in step (2). The composite pore-forming agent is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of 3.2:1, and the total addition amount is 12% of the mass of LiFePO4. During the programmed temperature rise process, 99.5% pure CO2 gas is introduced, with a CO2 flow rate of 5.5 mL / min at 200-300℃ and a CO2 flow rate of 20 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment of 100 Pa with a power of 270 W for 35 min.

[0048] Example 4

[0049] The only difference between this embodiment and Embodiment 1 in terms of materials is Mn. 2+ The doping amount was changed to 0.8 at%, and all other parameters remained the same.

[0050] Example 5

[0051] The only difference between this embodiment and Example 1 in terms of materials is that the conductive carbon black composition is changed to 75wt% nano carbon black + 25wt% micron carbon black, while the other parameters are exactly the same.

[0052] Example 6

[0053] The only difference between this embodiment and Embodiment 1 in terms of method is that the plasma power is changed to 280W, while the other parameters are exactly the same.

[0054] Example 7

[0055] The only difference between this embodiment and Example 1 in terms of preparation method is that the amount of KH-550 silane coupling agent added in step (2) is 0.3%, and the other parameters are exactly the same.

[0056] Example 8

[0057] The only difference between this embodiment and Example 1 in terms of preparation method is that the CO2 flow control in step (4) is changed to 3 mL / min at 200-300℃ and 8 mL / min at 300-400℃. All other parameters are exactly the same.

[0058] Example 9

[0059] The only difference between this embodiment and Example 1 in terms of preparation method is that the CO2 flow control in step (4) is changed to 7 mL / min at 200-300℃ and 22 mL / min at 300-400℃. All other parameters are exactly the same.

[0060] Comparative Example 1

[0061] The only difference between this comparative example and Example 1 in terms of materials is that the chemical formula of lithium iron phosphate is Li. 0.92 Fe 1.08 PO4, with all other parameters being exactly the same.

[0062] Comparative Example 2

[0063] The only difference between this comparative example and Example 1 in terms of method is that there is no Mn at the Fe site. 2+ Doped, all other parameters are exactly the same.

[0064] Comparative Example 3

[0065] The only difference between this comparative example and Example 1 in terms of method is that the CO2 flow rate stage control is cancelled in step (4), and the flow rate is kept constant at 5 mL / min throughout the process. All other parameters are exactly the same.

[0066] The conductive carbon black-modified lithium iron phosphate electrode materials provided in Examples 1-9 and Comparative Examples 1-3 were used to prepare lithium-ion battery cathodes, and their battery performance was tested. The results are shown in Table 1.

[0067] Table 1

[0068]

[0069]

[0070] Based on the comparative analysis of the above test data, we can draw the following conclusions:

[0071] (1) The key performance indicators of Examples 1-9, such as specific capacity, 5C capacity retention, 3000-cycle retention, compaction density, electronic conductivity, and lithium-ion diffusion coefficient, are significantly better than those of Comparative Examples 1-3, indicating that the present invention, by using Mn 2+ / Co 2+ Doping, the combination of dual-scale conductive carbon black, the covalent bonding of PC interfaces, and the gradient pore structure design significantly improve the energy density, rate performance, cycle stability, and structural stability of lithium iron phosphate electrode materials.

[0072] (2) Comparing Example 1 and Example 4, it can be seen that, due to the Mn in Example 4 2+Although the material cost is slightly reduced when the doping amount is reduced to 0.8 at%, the electronic conductivity is weakened, resulting in a decrease in specific capacity and 5C capacity retention to 153 mAh / g and 88%, respectively. This shows that the preferred doping range of 1-3 at% in this invention can effectively balance electrochemical performance and cost.

[0073] (3) Comparing Example 1 and Example 5, it can be seen that, due to the increased proportion of nano-carbon black in Example 5 to 75wt%, although the electronic conductivity increased to 1.8×10 -3 S / cm, but insufficient micronized carbon black caused the compacted density to decrease to 2.68 g / cm. 3 Furthermore, the cycle stability decreased slightly, indicating that the preferred 60-70 wt% nano carbon black ratio of this invention can balance conductivity and electrode processing performance.

[0074] (4) Comparing Example 1 and Example 6, it can be seen that since the plasma power of Example 6 is increased to 280W, the PC bonding density may increase slightly. However, the excessive power leads to partial carbonization of the material surface and the lithium ion diffusion coefficient is not significantly improved. This indicates that the preferred plasma treatment range of 230-270W in this invention can achieve a balance between interface optimization and material stability.

[0075] (5) Comparing Example 1 and Example 7, it can be seen that since the amount of silane coupling agent KH-550 added in Example 7 was reduced to 0.3%, the carbon black dispersion became worse, the electronic conductivity decreased to 0.9×10-3S / cm, and the cycle retention rate decreased to 82%. This shows that the preferred amount of 0.5-1% silane coupling agent added in this invention is crucial for the uniform construction of the conductive network.

[0076] (6) Comparing Examples 1 and 8-9, it can be seen that due to the low CO2 flow rate in Example 8, the gradient pore structure is not fully developed, and the lithium-ion diffusion coefficient drops to 2.9 × 10⁻⁶. -14 cm 2 / s; however, in Example 9, the CO2 flow rate was too high, and the surface porosity was too large, resulting in a decrease in compaction density, indicating that the preferred CO2 program flow control strategy of the present invention can accurately regulate the pore gradient distribution.

[0077] (7) Comparing Example 1 and Comparative Examples 1-3, it can be seen that Comparative Example 1 is due to Li 0.92 Fe 1.08 The stoichiometry of PO4 deviated from the preferred range, resulting in increased lattice defects and significant deterioration of specific capacity and lithium-ion diffusion coefficient; Comparative Example 2 did not undergo Mn treatment. 2+ Doping reduces electronic conduction and cycling stability; in Comparative Example 3, the absence of CO2 gradient pore formation resulted in uneven pore distribution and a 5C capacity retention rate reduced to 82%, further verifying the synergistic necessity of the various technical features of this invention.

[0078] The conductive carbon black-modified lithium iron phosphate electrode material of this invention significantly improves the electronic conductivity and structural stability of the material by optimizing the matrix stoichiometry, introducing transition metal doping, and constructing a two-scale conductive carbon black network. Simultaneously, through the covalent bonding of PC interfaces and the design of a gradient pore structure, efficient electrolyte wetting and rapid lithium-ion transport are achieved, thus maintaining high energy density while exhibiting excellent rate performance and long cycle life. This technical solution overcomes the problems of poor conductivity and interface instability in traditional lithium iron phosphate materials through the synergistic effect of various components and processes, providing an ideal electrode material solution for high-power, long-life lithium-ion batteries.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are still within the scope of the present invention.

Claims

1. A conductive carbon black-modified lithium iron phosphate electrode material, characterized in that, include: Li 1-x Fe 1+x The matrix is ​​PO4, where 0.01 ≤ x ≤ 0.05, and the Fe sites are doped with 1-3 at% Mn. 2+ or Co 2+ ; A conductive carbon black composition comprising 60-70 wt% nano-carbon black and 30-40 wt% micron-sized carbon black, wherein the nano-carbon black has a D50 ≤ 100 nm and a specific surface area ≥ 800 m². 2 / g, the micron-sized carbon black has a D50 of 1-3μm and a specific surface area ≥60m². 2 / g; Li 1-x Fe 1+x The PO4 particles are covalently bonded to conductive carbon black via PC, with a bond density ≥ 0.5 bonds / nm. 2 ; The material has a gradient pore structure, with a surface porosity of 25-30% and a pore size of 50-100 nm, and a core porosity of 15-20% and a pore size of 200-300 nm. The preparation method of the conductive carbon black modified lithium iron phosphate electrode material includes the following steps: (1) According to Li 1-x Fe 1+x The raw materials were mixed in stoichiometric proportions with PO4, and Mn was added. 2+ Salt or Co 2+ Salt was sintered at 650-750℃ for 6-8 hours to obtain doped LiFePO4 powder; (2) Mix nano-carbon black and micron-sized carbon black in a certain proportion, add silane coupling agent and ball mill for modification for 1.8-2.2 h. The silane coupling agent is KH-550 and the amount added is 0.5-1% of the total mass of carbon black. (3) The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a speed of 480-520 rpm for 2.8-3.2 h; (4) Mix the mixture obtained in step (3) with the composite pore-forming agent, and introduce CO2 gas during the programmed temperature rise process, wherein the CO2 flow rate is 4.5-5.5 mL / min at 200-300℃ and 10-20 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment with a power of 230-270W for 25-35 minutes.

2. The electrode material according to claim 1, characterized in that, The nano carbon black is acetylene black, and the micron carbon black is Super P.

3. The electrode material according to claim 1, characterized in that, The Mn mentioned in step (1) 2+ The salt is manganese acetate, and the Co 2+ The salt is cobalt nitrate, and Mn 2+ Salt or Co 2+ The amount of salt added is 1-3% of the molar amount of Fe.

4. The electrode material according to claim 1, characterized in that, The composite pore-forming agent mentioned in step (4) is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of (2.8-3.2):1, and the total amount of the composite pore-forming agent added is 8-12% of the mass of LiFePO4.

5. The electrode material according to claim 1, characterized in that, The purity of the CO2 gas mentioned in step (4) is ≥99.5%.

6. The electrode material according to claim 1, characterized in that, The pressure of the argon plasma treatment in step (5) is 50-100 Pa.

7. A lithium-ion battery positive electrode, characterized in that, The positive electrode is made using the conductive carbon black-modified lithium iron phosphate electrode material as described in claim 1, wherein the compaction density of the positive electrode is ≥2.7 g / cm³. 3 Capacity retention at 5C rate is ≥90%, and capacity retention after 3000 cycles is ≥85%.

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